An intensive effort has been made toward the development of non-ionizing radiation in the treatment of human neoplasms. These investigations have been guided by two biological principles: 1) the melanins have been found to be biologically amorphous semiconductors and have anomalously high ultrasound absorption coefficients, and 2) elevated temperatures in the 40-50 degrees C temperature range may have significant anti-tumor activity. In vitro studies using elevated temperatures between 41 degrees and 44 degrees C have demonstrated synergism between these temperatures and the chemotherapeutic drugs cis-platinum and mitomycin-C. The primary mechanism for the potentiation of these drugs was found to be inhibition of enzymatic removal of DNA cross-links created by these drugs. Plane wave ultrasound and localized alternating magnetic field systems have been developed and Phase I/II studies have been carried out in humans. The first 50 patients studied have shown an overall objective response rate of 55% for tumor temperatures between 42 degrees and 46 degrees C with no correlation between ultrasound and magnetic field dose and anti-cancer activity. All tumors treated above 47 degrees C responded. Fifteen patients were also treated with a combination of ultrasound and ionizing radiation; nine of these patients were diagnosed as malignant melanoma. The objective response rate with this form of therapy was 100% with a complete response rate of 60%.